Shortly after the initial symptoms of HPS appear excess fluid may accumulate in the lungs (pulmonary edema), beginning in the air spaces in the lungs (interstitial edema). Fluid may then fill the pockets in the lung tissue (alveolar edema) of both lungs (bilaterally) and cause difficulty in breathing and abnormally low levels of oxygen in the blood (hypoxemia). Accumulation of tissue and cells not normally found in the lungs (infiltrates) may also occur. The disease progresses rapidly and may cause abnormally low blood pressure (hypotension), shock, and/or respiratory distress.

Causes

HPS in the US is mostly caused by Sin Nombre Hantavirus, a newly identified virus within the Bunyaviridae family. The virus is carried by the deer mouse (Peromyscus maniculatus). The deer mouse can be found in most parts of the United States, except the southeast. Not all deer mice are infected with Sin Nombre hantavirus, and those that do carry the virus do not appear to be affected by any associated disease.

Three other species of hantavirus are causing human disease in the US: New York Virus identified in the white-footed mouse (eastern US), Black Creek Canal virus in cotton rat in Florida, and Bayou virus in Rice Field Mice in Texas and Louisiana. In addition, many other hantaviruses have been found in other rodent species in several States but were never detected in humans. In South America, numerous hantaviruses have been found responsible of human diseases. Andes virus is the cause of very severe HPS in Argentina and Chile.

Sin Nombre hantavirus is transmitted to humans when they come in direct or indirect (airborne) contact with waste products or saliva from an infected rodent. Respiratory transmission, thought to be the most frequent mode of transmission of Sin Nombre hantavirus, occurs when an individual inhales airborne particles of dust or dried particles that carry saliva or waste products from an infected rodent. Infectious virus particles could also penetrate through the mucosa.

Affected Populations

HPS appears to affect males and females in equal numbers. Approximately half of the cases reported in the medical literature have affected Native Americans, and the majority of the remaining reported cases affected Caucasians. The population affected by HPS appears to be related to geographic location and exposure to rodent droppings as opposed to ethnic background. Because many of the documented cases have occurred in the southwestern United States, a high percentage of the initially affected individuals were Native Americans. As the virus was found in others parts of the US, many others of varied ethnic backgrounds have been affected throughout the United States.

Related Disorders

Symptoms of the following disorders can be similar to those of Hantavirus Pulmonary Syndrome. Comparisons may be useful for a differential diagnosis:

There are many types of pneumonia that can be caused by bacteria or virus. In general the symptoms of pneumonia are similar to those of Hantavirus Pulmonary Syndrome. Only laboratory testing can determine which disease is affecting an individual.

Interstitial pneumonia, involving the spaces and tissue (interstices) of the lungs, is a type of primary pneumonia. It involves an abnormal increase in the interstitial tissue and a decrease and hardening (induration) of other lung tissue. Major symptoms may include shortness of breath on exertion, cough (which may or may not be present), and loss of appetite. Symptoms of interstitial pneumonia may vary from mild to severe according to the extent of lung involvement, accumulation of tissue and cells not normally found in the lungs (infiltrate), the rate of progress, and the presence of complications (such as other lung infections). The patient often has no fever (afebrile). However, occasionally the onset may be rapid, with fever, suggesting an acute respiratory infection. (For more information on this disorder, choose “Interstitial Pneumonia” as your search term in the Rare Disease Database.)

Eosinophilic pneumonia is characterized by an inflammation of the lungs and an abnormal increase in the number of certain white blood cells (eosinophils) in the lymph nodes, lungs, and blood. This disorder is usually associated with allergic conditions and various parasitic infections. Eosinophilic pneumonia usually has a sudden onset. There may be accompanying weight loss and increased pulse rate. Symptoms may also include low-grade fever, cough with the possibility of blood in the phlegm, wheezing and labored breathing. There may also be chills, sweating, chest pain, and/or a general feeling of ill health. The symptoms of eosinophilic pneumonia may be mild or severe, depending upon the amount of lung area affected. (For more information on this disorder, choose “Eosinophilic Pneumonia” as your search term in the Rare Disease Database.)

Standard Therapies

It is important to avoid areas where deer mice leave their droppings, such as storage sheds, basements, and wood piles. When exposed to mouse droppings, an individual should wear a face mask that covers both nose and mouth, as well as rubber gloves. The area should be sanitized with disinfectant to avoid aerosolization of potentially infected dust. People who exhibit flu-like symptoms after exposure to mouse droppings should be taken to a hospital immediately, because this disorder progresses over a matter of hours, and every hour is crucial.

The diagnosis of HPS depends on several factors, including the symptoms of the affected individual, a history of contact with rodents (especially deer mice) or exposure to areas where rodents may live, the lack of any alternative diagnosis, and/or laboratory tests that show characteristic changes. Because the symptoms of HPS are rapidly progressive, immediate aggressive care is indicated if HPS is suspected.

Characteristic laboratory blood test results for people with HPS may show abnormally enlarged white blood cells (atypical lymphocytes), a platelet count that is lower than normal (thrombocytopenia) or dropping, and/or a higher than normal white blood cell count. Oxygen levels in blood and/or tissue may be extremely low (hypoxemia).

The diagnosis of HPS is confirmed when laboratory tests reveal the presence and/or increased levels of certain proteins (Hantavirus IgM and/or a rising IgG titer) in blood samples from affected individuals. A process called polymerase chain reaction (PCR) may be used to detect a hantavirus and identify which strain has caused the infection.

Treatment of HPS involves intensive care, including the monitoring of fluid balances, electrolyte balances, and blood pressure. Abnormally low levels of oxygen in the blood (hypoxemia) may require the administration of oxygen. Shock and low blood pressure (hypotension) associated with HPS may be treated with drugs (i.e., dopamine and norepinephrine) to increase blood flow and thus improve blood and oxygen delivery to organs. In severe patients, Extra Corporeal Membrane Oxygenation (ECMO) therapy could be offered in specialized centers and may be the only chance of survival.

Investigational Therapies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:www.centerwatch.com

Centers for Disease Control and Prevention. Hantavirus Pulmonary Syndrome (HPS). Last Update February 6, 2013. http://www.cdc.gov/hantavirus/hps/. Accessed June 20, 2016.

Years Published

1994, 1995, 1998, 2000, 2009, 2012, 2016

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